1. Field of the Invention
This invention relates to a lens module, and more particularly, the invention relates to a lens module with adjustable magnification, which can be implemented with a corresponding correction lens and a primary lens by the selection, according to a dimension of the optical sensing device, such as the total length of the effective image pixels.
2. Description of Related Art
In the current modern life with the scientific technology in great and rapid development, the scanner has been an important apparatus in the daily life for the modern people. For example, the user can use the scanner to scan a document or a picture pattern, so as to capture the scanned image for the document or the picture pattern and store it as a backup. The scanned image can be further modified and enhanced if desired. It is very convenient.
In general, the scanner includes a light source, a primary lens, and an optical sensing device. When the scanner scans the document to be scanned, the light source will provide the light beam to illuminate the document and produce a scanning light beam. Next, the primary lens will collect and focus the scanning light beam and to form an image on the optical sensing device. Then, the optical sensing device will capture the scanned image from the document. Also, the size of the scanned image must satisfy the size specifications of the optical sensing device.
Referring to FIG. 1, it is a drawing schematically illustrating an optical path from the document to be scanned through the primary lens, and to the optical sensing device. As shown in FIG. 1, the primary lens 102 has a light collection end 102a and an image output end 102b, which are opposite to each other. The document to be scanned 106 is located at the outer side of the light collection end 102a, and the optical sensing device 104 is located at the outer side of the image output end 102b. In the scanning process, after the light source (not shown in FIG. 1) illuminates the document to be scanned 106, a scanning light beam 108 is produced. The primary lens 102 will collect the scanning light beam 108 via the image output end 102b and focus the light to form an image on the optical sensing device 104 located at the outer side of the image output end 102b. It is noted that the size of the scanned image captured by the optical sensing device 104 satisfies the size of the optical sensing device 104. It is assumed that the size of the document to be scanned 106 is L, and the size of the scanned image captured by the optical sensing device 104 and the size of the optical sensing device are equal to A. In this situation, the magnification of the primary lens 102 is A/L.
Generally, the size of the optical sensing device used by the current scanners is not always the same, which results in the need of an optical sensing device of different size to be implemented correspondingly with a primary lens by different magnification, so as to precisely capture the scanned image. Since this optical sensing device needs to be implemented with a primary lens, the manufacturer must specifically develop a corresponding primary lens to match the optical sensing device being used. This procedure would consume much development resource and increase fabrication cost.